In the field of hydraulic work machines, for example, hydraulic excavators, variable displacement hydraulic pumps are typically driven by an engine to provide hydraulic power to a plurality of work elements which includes the drive system. Excavators, being extremely versatile machines, are useful in performing a large number of different and varied tasks, e.g., pipelaying, mass excavation, trenching, logging, etc., each task having its own unique hydraulic flow and pressure requirements. For example, during mass excavation, hydraulic power requirements are quite high with brief periods of reduced need, but in pipelaying, sustained periods of low power during waiting are common with sessions of moderate to high power.
Rudimentary control schemes have been utilized to control the engine speed of an excavator. For example, these control schemes have shown that the engine speed may be reduced to low idle during sustained periods of waiting to conserve fuel. However, these types of control schemes do not recognize controlling the engine speed during active times where less than maximum engine speed and pump flow would be required.
More sophisticated control schemes have shown that the engine speed and hydraulic pump displacement can be controlled in response to loads subjected on the work vehicle. For example, U.S. Pat. No. 4,523,892 issued to Mitchell et al. on Jun. 18, 1985, discloses an electronic control system for a hydraulic excavator which controls the engine speed and pump displacement. The control system reduces pump displacement in response to the operating speed of the engine lugging below a desired operating speed. Further, the control system reduces the engine speed in response to the operating speed of the engine rising above the desired operating speed. In this manner, the electronic control adjusts for engine lag but the electronic control does not correct the inefficiencies of the system. Thus, the electronic control improves, but does not minimize fuel consumption or eliminate undesirable engine lag.
The present invention is directed to overcoming one or more of the problems as set forth above.